#### 2.1.2 TOdb

MetaQTL can also used a trait ontology in order to group the QTL in trait categories which refer to the same genetic determinism. The ontology representation handles by MetaQTL is based on a simple hierarchy (such as in taxonomy) where each child has a uniq parent. The table which stores the trait ontology is defined by the following fields:

- Term_id(integer): the uniq identifier of the term.
- Term_name(string): the name of the term, i.e the trait name.
- Parent_id(integer): the identifier of the uniq parent of this term (required except for the root of the ontology).
- Synonyms(string): the synonyms of the trait name separated by a coma (then the synonyms must not contain any coma).
- Definition(string): the definition of the trait.

         Term_id   Term_name   Parent_id   Synonyms   Definition
         1       my_ontology
         2       yield                   1
         3       dry_grain_yield_ear     2
         4       dry_grain_yield         2
         5       grain_yield             2
         6       kernel_weight_per_ear   2